Background：Thymidylate synthase catalyzes the methylation of deoxyuridylate to deoxythymidylate using 5,10-methylenetetrahydrofolate （methylene-THF） as a cofactor. This function maintains the dTMP （thymidine-5-prime monophosphate） pool critical for DNA replication and repair. The enzyme has been of interest as a target for cancer chemotherapeutic agents. It is considered to be the primary site of action for 5-fluorouracil, 5-fluoro-2-prime-deoxyuridine, and some folate analogs. Expression of this gene and that of a naturally occuring antisense transcript rTSalpha （GeneID：55556） vary inversely when cell-growth progresses from late-log to plateau phase.
